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Not Applicable
1. Field of the Invention
The present invention relates generally to a self-calibrating system and method for controlling a hydraulically operated device, and more particularly to a self-calibrating system and method for controlling an actuator employed in an automatic power transmission.
2. Description of the Related Art
Hydraulically operated devices or actuators are employed in a wide variety of applications including, but not limited to, vehicle applications. For example, hydraulic actuators are used in automatic power transmission systems and variable assist power steering systems. Recently manufactured vehicles use an electronic control module (ECM) which often operates with additional electronic control modules like a transmission control module (TCM) for effecting shift control of the transmission. The TCM may be integrated into the ECM, or as a separate unit located on the vehicle outside the transmission. Some manufacturers intend to position the TCM inside the transmission.
An ECM and TCM contain microprocessors with programmable control logic and may be implemented in a variety of combinations of hardware and/or software circuitry components known in the art to control the various vehicle systems or subsystems, operating in conjunction with hydraulically operated devices. When a TCM receives a command signal to adjust the hydraulic fluid pressure for an actuator, the TCM sends a current signal to an electrically operated hydraulic valve. The hydraulic valve in response thereto adjusts the pressure for hydraulically controlling a device like a clutch piston.
Currently, TCMs are manufactured independently of the hydraulic components they are designed to control. The TCMs are designed with tight tolerances on the current output and the hydraulic components are calibrated to achieve a desired hydraulic pressure output band (tolerance) for a given current input. Even with the tight tolerances, the hydraulic output pressure varies considerably from transmission device to transmission device. When the current signal tolerance is added to the hydraulic pressure tolerance of the device, a significant difference between the commanded pressure and the actual pressure output can result. The same desired pressure electrical command given to two different TCMs can yield different hydraulic pressure outputs.
Consequently, there is a need for a system and method for controlling a hydraulic device that automatically self-calibrates. The self-calibrating system and method preferably provides constant feed-back to adjust to the hydraulic circuit to reduce and even eliminate tolerance and wear effects. In this way, the system and method will verify that the actual pressure is fairly close to the desired pressure.
Accordingly, an object of the present invention is to provide a method for automatically calibrating a hydraulic control system.
Another object of the present invention is to provide a self-calibrating system for controlling a hydraulically operated device.
A further object of the present invention is to provide a self-calibrating system for controlling a hydraulically operated device for use in an automatic power transmission.
The above and other objects of the present invention are accomplished with a method that automatically calibrates a hydraulic control system. The method of the present invention comprises the steps of providing a source of hydraulic fluid pressure and supplying the fluid pressure to the inlet of an electrically operated pressure control valve, connecting the outlet of the pressure control valve to a hydraulically operated actuator, providing a controller with control logic and memory, connecting the controller to the pressure control valve, electrically energizing the pressure control valve with a control signal from the controller and providing a controlled hydraulic fluid pressure through the valve outlet to the actuator, sensing the pressure of the hydraulic fluid pressure and at a set point level providing a signal indicative thereof to the memory of the controller and storing the same in memory, measuring an amount of current to the pressure control valve necessary for the fluid pressure to reach the set point level, comparing the measured current with a preset value of the current as a function of the pressure signal, and adjusting the control signal based upon the current comparison for automatically calibrating the hydraulic control system.
The self-calibrating system for controlling a hydraulically operated device in accordance with the present invention comprises a hydraulically operated actuator, a pump connected to said actuator for providing a source of pressurized hydraulic fluid, an electrically actuated pressure control valve disposed between the pump and the actuator, and fluidly connected therebetween, the control valve being operative to receive a hydraulic fluid at a supply pressure and provide the hydraulic fluid at a control pressure at the valve outlet, a controller having control logic and a memory in communication with the pressure control valve, the controller being operative for providing a control signal for actuating the pressure control valve, a pressure sensor for sensing the hydraulic fluid pressure disposed between the pressure control valve outlet and the hydraulically operated actuator, the pressure sensor being in communication with the controller and operative to provide a signal to the controller when the sensed pressure reaches a predetermined level, the controller being operative to store the signal in the memory and to measure an amount of current to the pressure control valve resulting from the control signal, and the controller being operative to compare the measured current with a calibrated value of current as a function of the pressure, wherein the controller is operative to adjust the control signal based upon the comparison.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is described and illustrated.